A common drawback of clips of this type is that the resistance to withdrawal of the pipe or similar article or component is directly proportional to that of insertion. That is, the resistance to withdrawal of the pipe or similar, article or component which should be as high as possible to ensure effective retention, cannot be increased without causing a corresponding increase in the resistance to insertion, which on the other hand should be as low as possible. As a result, to ensure sufficiently safe retention, the resistance to insertion is such as to seriously impede assembly of the pipe or similar article or component.
It has been proposed, for example in German Patent No. 3,002,031, to divide the flexible wall defining the seat into two separate, substantially concentric parts, the main purpose of which being to enable the clip to accommodate pipes or similar articles or components of different sizes, and to protect the retaining wall against stones thrown up by the vehicle. The inside of the wall cooperating directly with the pipe or similar article or component is relatively highly flexible so as to adapt to pipes or similar articles or components of widely differing diameters, while the outside of the wall not cooperating directly with the pipe or similar article or component acts as a protective shield. Although the flexural strength of both parts of the wall provides for retention, and both parts of the wall cooperate to prevent withdrawal of the pipe or similar article or component--in the presence of a force tending towards withdrawal, the inside of the wall rests against the outside--the above solution fails to provide for reducing the resistance of the clip to insertion of the pipe or similar article or component inside the seat, which resistance still remains proportional to the withdrawal resistance.